The present invention relates to an image or video data processing system which records image or video signals based on a compression coding technique, and more particularly to an image or video data processing system which is preferably applied to recording and reproduction of image or video signals supplied from video cameras of a monitoring system.
According to a conventional monitoring system, a switcher is provided to selectively switch video signals of a plurality of monitor cameras and a main recording medium is provided to store the selected video signals. In this case, the video signals are converted into digital signals and processed according to an image compression technique so as to realize high quality and low cost image recording and/or reproduction.
Regarding the techniques for compressing motion pictures or time-varying images, a conventionally well known one is the MPEG (i.e., motion picture expert group) technique which utilizes a correlation of frames to reduce an overall data amount. According to the MPEG technique, differential components or correlation between two time serial frames are subjected to a discrete cosine transformation (i.e., DCT) or the like to obtain two-dimensional frequency components. The two-dimensional frequency components thus converted are subsequently subjected to a variable length encoding so as to reduce the overall data amount.
According to the MPEG technique, when a difference between two time serial frames is motionless or very small, a required data amount can be suppressed to a very small value. When the difference between two time serial frames is large, a compensation is performed based on motion vectors between two frames. Thus, the image quality can be maintained at satisfactory levels even when the compression efficiency is high.
In general, the monitoring system should respond to various requirements. For example, it is desirable to quickly and smoothly reproduce intended images stored in the main recording medium in accordance with user""s designation of a specific monitor camera or a specific time. However, recoding the video signals according to the MPEG technique is inherently dependent on the correlation between two frames which are mutually time serial. In other words, the MPEG technique is a sort of prediction coding relying on the image or video data of an immediately preceding frame. Thus, when any specific image of a specific time is required, it is definitely necessary to start the reproducing operation from a fundamental frame and time sequentially perform the reproduction of succeeding frames. Otherwise, the intended image cannot be reproduced. It is fairly time consuming and complicated.
Furthermore, the main recording medium, such as a hard disk, is an internal or built-in memory which has a huge recording capacity. The image or video data processed by the compression technique is stored in the main recording medium and exclusively used for displaying the recorded images on a monitor television. It was generally difficult to reproduce the recorded image or video data by an external device.
In view of the foregoing problems, the present invention has an object to provide an image or video data processing system which is capable of easily searching an intended image or video data from the main recording medium and is capable of easily transferring the recorded image or video data to an external recording medium.
To accomplish the above and other related objects, the present invention provides an image or video data processing system comprising in-frame encoding means for performing in-frame compression for each frame of input image or video data to obtain in-frame compression data, recording means for storing the in-frame compression data, in-frame decoding means for reading out the in-frame compression data from the recording means and obtaining reproduced image or video data, compression converting means for reading out a plurality of in-frame compression data from the recording means and converting the readout plurality of in-frame compression data into an inter-frame compression data, and output control means for outputting the inter-frame compression data to an external device.
With this arrangement, the recording means stores the in-frame compression data for each frame of the input image or video data. The reproducing operation can be easily performed by searching a designated frame. When the recorded data is output to the external device, the in-frame compression data read out from the recording medium is subjected to the inter-frame compression by utilizing the correlation between frames. Thus, it becomes possible to realize a long-term recording of high quality image or video data for a recording medium having a relatively small recording capacity. Furthermore, it becomes possible to transmit the high quality image or video data via a transmission path having a relatively narrow band.
Furthermore, according to the image or video data processing system of the present invention, it is preferable that the input image or video data are time serially mixed data picked up by a plurality of image pickup means, the in-frame encoding means successively compresses the time serially mixed data for each frame to obtain the in-frame compression data, and the recording means stores an identification code of a corresponding image pickup means together with each in-frame compression data.
With this arrangement, a plurality of image or video data are successively compressed frame by frame and stored in the recording means. The reproducing operation can be easily performed by searching a designated frame. Furthermore, as the identification code of an image pickup means is recorded to together with corresponding in-frame compression data, the reproducing operation can be easily performed by searching a designated image pickup means.
Furthermore, according to the image or video data processing system of the present invention, it is preferable that the image pickup means is mounted on a rotary table, and the recording means stores a position code representing a position of the camera mounted on the rotary table together with the identification code. The position code includes various information, such as horizontal position, vertical position, zoom, focus etc.
With this arrangement, the identification code and the position code of an image pickup means are stored together with the corresponding in-frame compression data in the recording medium. Thus, it becomes possible to easily search the recorded image or video data for each image pickup means by designating both the identification code and the position code of this image pickup means.
Furthermore, according to the present invention, it is preferable that the image or video data processing system further comprises data size gaining means for detecting an original data size of the in-frame compression data read out from the recording means, recording capacity gaining means for detecting an available recording capacity of a portable recording medium storing the inter-frame compression data under control of the output control means, and code amount control means for calculating a target compression rate based on the original data size of the readout in-frame compression data detected by the data size gaining means and the recording capacity of the portable recording medium detected by the recording capacity gaining means. The code amount control means controls the compression converting means based on the calculated target compression rate so as to equalize a data amount of the inter-frame compression data with the available recording capacity of the portable recording medium.
With this arrangement, it becomes possible to control a total data amount of the inter-frame compressed image or video data. Thus, a recording amount of the compressed data in a portable recording medium can be surely predicted.
Furthermore, according to the present invention, it is preferable that the image or video data processing system further comprises general interface means for transmitting the in-frame compression data read out from the recording means to the compression converting means which has a capability of judging image or video data.
With this arrangement, presence of the general interface means makes it possible to separately arrange the portion including the recording means from the portion including the compression converting means. Using the general interface makes it possible to judge image or video data. When no fetching of the inter-frame compression data is required, it becomes possible to remove a portion accommodating the compression converting means. Therefore, it becomes possible to suppress increase of system costs.
Furthermore, according to the image or video data processing system of the present invention, it is preferable that the compression converting means converts the in-frame compression data into the inter-frame compression data according to the MPEG2 technique, and the output control means records the inter-frame compression data into a DVD-RAM disk with a format conformable to a DVD video recording standard.
With this arrangement, when the MPEG2 technique is used to perform the inter-frame compression data, the inter-frame compressed data can be recorded into a DVD-RAM disk according to the format conformable to the DVD video recording standard. This makes it possible to easily reproduce the recorded image or video data on a personal computer or a comparable home-use reproducing or playback device.